Data communication system and method

ABSTRACT

A data communication system includes one or more data processing units and includes a central control unit. The decentralized data processing units are connected to the central control unit by data connection. The central control unit includes a synchronisation unit for outputting via the data connection an electric synchronisation signal to the data processing unit. The data processing unit includes a data generator for generating data and transmitting, after the electric synchronisation signal, data to the central control unit. The central control unit further includes a discharge signal generator for outputting a discharge signal via the data connection to the data processing unit.

FIELD OF THE INVENTION

This invention relates to a data communication system. The inventionfurther relates to a central control unit. The invention also relates toa data processing unit, and to a vehicle. The invention further relatesto a method for communicating data. The invention further relates to acomputer program product.

BACKGROUND OF THE INVENTION

From U.S. Patent Application Publication US 2006/0080495, a datacommunication system is known. The data communication system has acentral control unit, decentralized data processing units and a dataconnection between the central control unit and the decentralized dataprocessing units. During the transmission, in order to request datapackets, the central control unit periodically outputs synchronizationpulses over the data connection to the data processing unit interface,whereupon the decentralized data processing unit transmits data packetsto the central control unit. The decentralized data processing unitgenerates an electrical discharge pulse after the synchronization pulsebut before the transmission of a first data packet, therebycounteracting an electrical charging of the data processing unitinterface by the synchronization pulse.

However, the duration of the electrical discharge pulse has to besufficiently long to take into account possible mismatches in timingbetween the central control units and the decentralized data processingunits. Since the power consumption of the system is determined, interalia, by the duration of this pulse, a disadvantage of the datacommunication system described in this Patent Application Publication istherefore that the electrical discharge pulse consumes a significantamount of power.

SUMMARY OF THE INVENTION

In accordance with a first aspect of the present invention a datacommunication system as described in the accompanying claims isprovided.

In accordance with a second aspect of the present invention a centralcontrol unit is provided.

In accordance with a third aspect of the present invention a dataprocessing unit is provided.

In accordance with a fourth aspect of the present invention an occupantprotection system is provided.

In accordance with a fifth aspect of the present invention a vehicle isprovided.

In accordance with a sixth aspect of the present invention a method forcommunicating data is provided.

In accordance with a seventh aspect of the present invention a computerprogram product is provided.

Specific embodiments of the invention are set forth in the dependentclaims.

These and other aspects of the invention will be apparent from andelucidated with reference to the examples of embodiments describedhereinafter

BRIEF DESCRIPTION OF THE DRAWINGS

Further details, aspects and embodiments of the invention will bedescribed, by way of example only, with reference to the attacheddrawings.

FIG. 1 schematically shows a block diagram of an example of anembodiment of a data communication system in accordance with theinvention.

FIG. 2 schematically shows examples of graphs of signals that may betransmitted by the example of FIG. 1.

FIG. 3 schematically shows a circuit diagram of an example of anembodiment of a central control unit in accordance with the invention.

FIG. 4 schematically shows a circuit diagram of an example of asynchronisation unit.

FIG. 5 schematically shows a circuit diagram of an example of anembodiment of a data processing unit in accordance with the invention.

FIG. 6 schematically shows a block diagram of an example of anembodiment of a restraint system in accordance with the invention.

FIG. 7 schematically shows a top view of an example of a vehicle with arestraint system in accordance with the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In FIG. 1, an example of a data communication system 1 is shown. Thedata communication system 1 includes a central control unit 10 and oneor more, in this example two, data processing units. The datacommunication system 1 further includes one or more data connections30,31. The data connections 30,31 connect the data processing units 20to the central control unit 10.

As shown in FIG. 3 in more detail, the central control unit 10 mayinclude a synchronisation unit 11. The synchronisation unit 11 mayoutput via the data connection 30,31 an electric synchronisation signalto one or more of the data processing units 20. By means of thesynchronisation signal, the time base of the data processing units 20 issynchronised. As shown in FIG. 5 in more detail, the data processingunit 20 includes a data generator 22. The data generator 22 can generatedata and transmit, after the synchronisation signal, the data to thecentral control unit 10, for example in order to transmit informationobtained by a sensor or other suitable information to the centralcontrol unit 10.

The synchronisation signal may affect the data connection 30,31. More inparticular, the data connections 30,31 may, as in the example of FIG. 1,include electrical connections and the synchronisation signal may be anelectrical signal, such as a change in voltage, in which case the dataconnection and/or the interface of the data processing unit receivingthe signal will be in a non-steady state during transmission of thesynchronisation signal.

For instance, in case the synchronisation signal is a voltage signal,such as a voltage pulse, the voltage of the data connection 30,31 willdeviate from the steady state voltage during transmission of thesynchronisation signal. Due to the voltage of the synchronisationsignal, the data connection 30,31 and/or the respective interfacesbetween the data connection 30,31 and the data processing units 20 willbe charged by the synchronisation signal. Accordingly, after the centralcontrol unit 10 has terminated the transmission of the synchronisationsignal, the charge on the data connection 30,31 delays the return of thevoltage of the data connection to the steady-state level. Thereby,synchronization of the data processing units 20 may be affected, sincethe termination of the synchronisation signal data cannot be determinedaccurately by the data processing units 20. Furthermore, when thevoltage of the data connection 30,31 is not at the steady state levelthe transmission of the data from the data processing units may beaffected. Accordingly, the period of time available for transmission ofdata from the data processing units to the central control unit isreduced by the charging of the data connection. The synchronisationsignal may, for example, charge capacitances in the data connection30,31 or in the data processing units 20. In the circuit diagram shownin FIG. 5, for instance, the capacitive elements are represented, forillustrative purposes, by a separate capacitor C20. However, thecapacitance may also be an integral part of, for example, the dataconnection 30 or the data processing unit 20 and not be present as aseparate element but for example caused by inherent, parasitic,capacitances.

As shown in the example of FIG. 3, the central control unit 10 mayinclude a discharge signal generator 14. The discharge signal generator14 can output a discharge signal via the data connection 30,31 to thedata processing unit 20. The discharge signal discharges the dataconnection 30,31 and/or the interface of the respective data processingunit(s) 20 connected to the data connection 30,31 over which thedischarge signal is sent, thereby accelerating a return to steady stateof the data connection 30,31. Accordingly, a smaller margin of timebefore starting the transmission may be used and the period of timeavailable for transmission of the data from the data processing units tothe central control unit may be increased. Furthermore, the dischargesignal is sent from the central control unit 10 to the data processingunits 20, accordingly the need to account for timing mismatches isobviated and the discharge signal may have a shorter duration. Thereby,the amount of power consumed by the transmission of the discharge signalcan be reduced. The discharge signal may for example be a current whichunloads capacitive elements in the data connection or in the dataprocessing units 20. For example, the synchronisation signal may be avoltage pulse and the discharge signal may be a current pulse, as forexample illustrated in FIG. 2.

FIG. 2 schematically illustrates an example of the development (as afunction of time) of the voltage V_(L) of the data connection 30, thecurrent I_(s) transmitted from the data processing unit 20, the currentI_(c) transmitted from the central control unit 10 and the total currentI_(t) flowing through the data connection 30. As shown in FIG. 2, thesynchronisation unit 11 may output a synchronisation signal SYNC to thedata processing units 20 connected to the data connection 30,31. Thesynchronisation signal may, for example, be outputted periodically, suchas after a period of time above 0.1 milliseconds and below 1millisecond, such as 0.5 milliseconds or less, for instance every 0.25milliseconds. In the example of FIG. 2, the synchronisation signal is avoltage pulse superimposed on a DC voltage level. The DC voltage may forexample be a DC offset voltage suitable to supply power to the dataprocessing units 20. For illustrative purposes, the synchronisationsignal is exaggerated in FIG. 2. The voltage for the DC offset voltagemay for example be in the range from 5 to 7 volts, such as 6 volts forinstance. The voltage of the synchronisation signal may for example be avoltage about the same or slightly less than the DC offset voltagesuperimposed on the DC offset voltage. The combined voltage of thesynchronisation signal and the DC offset voltage may for example be inthe range from 10 to 12 volts, such as 11 volts. However, other voltagesmay also be used.

As shown in FIG. 2 with the dashed line, without discharging signal, thereturn of the voltage of the data connection 30 to the DC offset levelafter the synchronisation signal has been sent, would be delayed due tothe charging of the data connection 30. The synchronisation unit 11 inthe central control unit 10 enables a current to flow, during a periodof time denoted with I in FIG. 2, through the data connection 30 whenthe synchronisation signal starts to decay, thereby discharging the dataconnection 31 and facilitating the return of the voltage level of thedata connection 31 to the steady state voltage level. After the voltageof the data connection 31 has returned to the steady state voltagelevel, the respective data processing unit 20 transmits data, during aperiod of time denoted with II in FIG. 2, to the central control unit 10by transmitting one or more binary signals over the data connection 30.In this example, the binary signal is formed by a current pulse. Thecurrent pulse and/or the synchronisation signal may for example be acurrent which flows from the data processing unit 20 to the centralcontrol unit 10 or vice versa.

The central control unit 10 may be implemented in any manner suitablefor the specific implementation. An example of an embodiment of acentral control unit 1 is shown in FIG. 3. The central control unit 10may, as shown in FIG. 3, include a synchronisation control unit 11. Thesynchronisation control unit 11 may for example include a timer 12, asynchronisation signal generator 13 and the discharge signal generator14.

In the example of FIG. 3, the synchronisation signal generator 13 isconnected with a signal generator input 130 to a clock signal output 120of the timer 12. The synchronisation signal generator 13 is furtherconnected with a generator output 131 to the data connection 30. In thisexample, the timer 12 periodically outputs a pulsed clock signal. Basedon the clock signal received from the timer 12, the synchronisationsignal generator 13 outputs a synchronisation signal. The dischargesignal generator unit 14 may, as shown in the example of FIG. 3, beconnected with a discharge signal generator input 140 to the timeroutput 12, in order to trigger the generation of the discharge signal.

The synchronisation signal generator 13 may be implemented in any mannersuitable for the specific implementation. The synchronisation signalgenerator 13 may, as for example shown in FIG. 3, include two or moredifferent voltage supplies Vs1,Vs2 which are at different voltages, anda switch S13 which can connect a selected voltage supply to thegenerator output 131. In the example of FIG. 3, for instance, the switchS13 is connected with a first contact at a first switch side to the lowvoltage supply Vs1 and with a second contact at the first switch side tothe high voltage supply Vs2. (For illustrative purposes, the voltagesupplies Vs1,Vs2 are shown in FIG. 3 connected to ground GND viarespective capacitors C11,C12.) The high voltage supply Vs2 is at ahigher voltage than the low voltage supply Vs1. A contact at a secondside of the switch S13, opposite to the first switch side, is connectedto the generator output 131, in this example via a resistor R13.Depending on the state of the switch S13, the first contact or thesecond contact is electrically connected to the contact at the oppositeside, and hence either the first voltage supply Vs1 or the secondvoltage supply Vs2 is connected to the contact at the second side of theswitch, and hence to the signal generator output 131. The state of theswitch S13 is controlled by the clock signal inputted at the signalgenerator input 130. In case the clock signal is low, the low voltagesupply Vs1 is connected to the generator output 131. In case the clocksignal is high, the high voltage supply Vs2 is connected to thegenerator output 131. Hence, the voltage of the signal generator output131 is controlled by the clock signal. As illustrated in FIG. 3, theinputted signal may have a pulsed shape, and accordingly, the voltage ofthe signal generator output 131 may change in a pulsed manner.

The discharge signal generator 14 may be implemented in any mannersuitable for the specific implementation. For instance, as shown in FIG.3, the discharge signal generator 14 may include a switch S14 whichconnects the data connection 30 to ground GND, for example, via acurrent source I. The discharge signal generator 14 further has a switchcontrol 141 which can receive the clock signal via the discharge signalgenerator input 140. The switch control 141 closes the switch S14 inresponse to the clock signal via a switch control input 143. The closedswitch S14 allows the current source I to draw current from the dataconnection 30 and hence discharging the data connection 30. However, thedischarge signal generator 14 may also be implemented in a differentmanner, and for example include a current source which can be switchedon and off and which draws a current from the data connection 30.

The operation of the discharge signal generator 14 may be coordinatedwith respect to the operation of the synchronisation signal generator13. For example the switch S14 in the discharge signal generator 14 maybe closed in response to switching of the synchronisation signalgenerator 13 from the high voltage supply Vs2 to the low voltage supplyVs1. Thereby, the data connection 30 may be discharged a short period oftime after the transmission of the synchronisation signal.

The synchronisation unit 11 may, as for example shown in FIG. 4, includea sensor for sensing a parameter of the data connection 30,31 and/or thedata processing unit 20. As shown in FIG. 4, the data connection 30 mayfor example be connected to a sensor input 151, to sense a parameter ofthe data connection 30. The sensor may for example include a voltagesensor which can sense the voltage of the data connection 30.

The synchronisation unit 11 may for instance include a circuit in whichthe sensor, and/or the synchronisation signal generator and/or thedischarge signal generator are combined. The signal generator 11 may, asshown in FIG. 4, for instance include a comparing unit 15. As shown inFIG. 4, a first comparing unit input 150 of the comparing unit 15 may beconnected to a reference source (not shown in FIG. 4) which provides areference signal representing the desired output voltage of thesynchronisation unit 11. At the first comparing unit input 150 a pulsedreference signal may be inputted, for example with pulses at regulartime intervals. A second comparing unit input 151 of the comparing unit15 may be connected with a feedback loop to the data connection 30, thusforming a sensor.

The comparing unit 15 may for example include a comparator which isconnected with a first input to a signal source which provides areference signal and which is connected with a second input to the dataconnection 30 and outputs a binary signal, e.g. either a positive signalor a negative signal with a constant amplitude. The comparator may forexample output the positive signal in case the voltage at the firstinput is higher than the voltage at the second input and output thenegative signal in case the voltage at the first input is lower than thevoltage at the second input. In such case, in case the voltage of thedata connection 30 exceeds the reference signal, the negative signal isoutputted by the comparator and in case the voltage of the dataconnection 30 is lower than the reference signal, the positive signal isoutputted by the comparator. Accordingly, outputting of thesynchronisation signal and the discharging signal can be controlled.

The synchronisation unit 11 may output the discharge signal based on thesensed parameter. As shown in the example of FIG. 4, the comparing unit15 may for instance control an output stage of the synchronisation unit11 based on the sensed parameter. In the example of FIG. 4, the outputstage includes a push-pull output stage. The control inputs of thepush-pull stage are formed by the control terminals G10 and G20 oftransistors T10,T20. The transistors T10,T20 connect the data connection30 to a power supply Vs and to ground, respectively. The transistorsT10,T20 are connected to each other with respective terminals D10 resp.D20 at a node V11 which is also connected to the data connection 30. Aterminal S10 of a respective transistor T10 is connected to the powersupply Vs and a terminal S20 of a respective transistor T20 is connectedto ground. In the example of FIG. 4, an output 152 of the comparing unit15 is connected to control inputs G10,G20 of the output stage of thesynchronisation unit 11. The output signal of the comparing unit 15controls the output stage, and hence the voltage and/or current of thedata connection 30.

The transistors T10,T20 of the push-pull output stage may for example beoperated in active mode. With the signal presented at the comparing unitoutput 152, the control terminals G10,G20 of the transistors T10,T20 canbe controlled, and accordingly the voltage drop between an inputterminal S10, D20 and an output terminal D10,S20 of a respectivetransistor T10, T20 can be regulated, as well as the current flowingbetween the input terminals and the output terminals. Thereby thevoltage of the data connection 30 can be controlled, as well as thecurrent flowing from the data connection 30 to ground GND via thetransistor T20.

In the example of FIG. 5, the transistors T10,T20 are connected suchthat they form a push-pull regulator. In case the output of thecomparing unit 15 increases, the voltage drop over the first transistorT10 decreases and the voltage drop over the second transistor T20increases, and hence the voltage of the data connection 30 increases. Incase the output of the comparing unit 15 decreases, the voltage dropover the first transistor T10 increases and the voltage drop over thesecond transistor T20 decreases. Hence the voltage of the dataconnection decreases. Furthermore, in case the comparing unit outputdecreases, the current through the second transistor T20 increases, andhence the data connection 30 can be discharged. Hence, the comparingunit output controls the synchronisation signal and the discharge signalsimultaneously.

The synchronisation unit 11 may for example be arranged to control themagnitude of the discharge signal and/or the synchronisation signalbased on a sensed parameter, e.g. the sensed voltage, of the dataconnection 30. The amplitude may for example be controlled to belinearly or non-linearly dependent on the difference. The comparing unit15 may for example include a differential amplifier which is connectedwith a positive input to a signal source which provides a referencesignal and which is connected with a negative input to the dataconnection 30. Thereby, the amplitude of the signal outputted by thecomparing unit 15 (which may be used to control the push-pull stage, asshown in the example) may be proportional to the difference between theamplitude of the reference signal and the voltage of the data connection30. In the example of FIG. 4, by means of the second comparing unitinput 151, the voltage at the first data connection 30 can be sensed bythe comparing unit 15, and the comparing unit 15 may hence be regardedas sensor. In this example, the comparing unit 15 senses the voltage ofthe data connection 30, which is fed back to the comparing unit input151 via a feedback line. The comparing unit 15 compares the sensedvoltage with a reference voltage inputted at the first inputs 150 andoutputs a signal which is proportional to the difference between thesensed voltage and the reference voltage. The output signal of thecomparing unit 15 is inputted to the control terminals G10, G20 of thepush-pull output stage and thereby the synchronisation signal and thedischarge signal are controlled together and simultaneous. Thereby, amore accurate control of the discharge signal may be obtained and theduration and or magnitude of the discharge signal may be reduced.

In the example of FIG. 4, the voltage of the data connection 30 and thecurrent flowing from the data connection to ground GND are controlled asa function of the voltage on the data connection 30 (and, in thisexample, the reference voltage). Thereby, the data connection may bedischarged in a controlled manner and in short period of time, since theneed to account for possible differences in voltage and/or duration ofthe synchronisation signal is obviated. In case, for example, the sensedvoltage is below the reference voltage, the comparing unit 15 willcontrol the control terminals G10,G20 to increase the voltage dropbetween the node V11 and ground GND and to decrease the voltage dropfrom the power supply Vs to the node V11. (For example by increasing theconductance from one terminal D10 to another terminal S10 and/ordecreasing the conductance between the node V11 and ground GND) In case,for example the sensed voltage is above the reference voltage, thecomparing unit 15 will control the control terminals G10,G20 to decreasethe voltage drop between the node V11 and ground GND (for example byincreasing the conductance from one terminal D20 to another terminal S20and/or decreasing the conductance between the voltage supply Vs and thenode V11 and hence allowing more current to flow from the dataconnection 30 to ground GND). The control will further increase thevoltage drop from the power supply Vs to the node V1.

FIG. 5 schematically shows an example of a data processing unit 20,which may be used in the example of FIG. 1. The data processing unit 20may, as shown in FIG. 5, include a sensor 22 which generates data to betransmitted to the central control unit 10.

The data connections 30,31 may, as explained above, be electricalconnections. For example, a data connection 30 may be set to a highvoltage and the other data connection 31 may be set to a low voltage,that is: a voltage lower than the high voltage. In the example of FIG.1, for instance a data connection 31 acts as ground (e.g. is set to zerovolts) whereas the other data connection is set to a suitable supplyvoltage. Thereby electrical power can be supplied to the data processingunits 20,21 over the same line as used to transmit the data. As shown inFIG. 5, the data connection 30 may for instance be set to a high voltageand connected to a power supply contact 210 of the sensor 22 as well asto a signal input 211 thereof.

The data processing unit 20 may include more than one sensor. However,the data processing unit 20 may include one or more other sources ofdata, and the invention is not limited to application in sensor systems.The sensor 22 may for instance include an acceleration sensitive sensor,such as an acceleration or deceleration sensor which may be used in anoccupant protection system in a vehicle, such as a motor vehicle.However, other types of sensor may be used, such as for instance apressure sensor, a temperature sensor which can detect, for instance, atemperature increase in a cavity which is compressed during an accident,such as the space inside the door of a motor vehicle.

The data processing unit 20 may include a data transmitter 21, which inthe example of FIG. 5 includes a current source I2 and a controllableswitch S20. The switch S20 can alternately enable and inhibit the flowof current from data connection 30, via source I2, in this example toground. The state of the switch is controlled via a switch control input212 which is connected to the sensor 22. By alternately opening andclosing the switch, the current through the data connection 30 can becontrolled, and hence a current signal be transmitted to the centralcontrol unit 10.

A data communication system in accordance with the invention, such asthe example of a data communication system 1 shown in FIG. 1, may forexample be used in an occupant protection system. The occupantprotection system may for instance include a restraint system or othersuitable type of protection system. A restraint system generally refersto a system designed to hold a person within the body of a vehicle andlimit movement during a crash, thereby reducing severity of injury. Theoccupant protection system may for example include a data communicationsystem in accordance with the invention, such as the example shown inFIG. 1, and one or more actuators connected to the central control unit10 to actuate a restraint device. The restraint device may for exampleinclude an airbag, a seat belt pre-tensioning device or other restraintdevice. FIG. 6 schematically shows an example of a restraint system 60.The restraint system 60 includes a restraint device 50, and an actuator51. The actuator 51 is connected to the central control unit 10. Thecentral control 10 may transmit an activation signal to the actuator 51,which may for example be an airbag actuator. The actuator may actuatethe restraint device 50 in response to the activation signal. Forexample, if the data processing unit 20 includes an acceleration sensor,the central control unit, in case the sensor or sensors senses anacceleration above a predetermined activation threshold, the centralcontrol unit 10 may transmit the activation signal. In response to theactivation signal, the actuator 51 may then activate the restraintdevice 50, e.g. the airbag 50. In the example of FIG. 5, only onerestraint device 50 and actuator 51 are shown. However, the system 60may include more than one restraint device 50 and more than one actuator51, which may be controlled separately by the central control unit 10.

FIG. 7 shows an example of vehicle 70 provided with an occupantprotection system. The example shown in FIG. 7 includes restraintdevices, 50, in this example airbags, connected via a suitable dataconnection 40,41 to a data communication system 1, for instance theexample shown in FIG. 6. As explained with reference to FIG. 5, thecentral control unit 10 may be arranged to control the actuator 51 basedon data received from the data processing unit 20 and control actuationof the inflation of the airbags, thus protection the occupants of thevehicle 70 against impact, for example during a crash.

In the foregoing specification, the invention has been described withreference to specific examples of embodiments of the invention. It will,however, be evident that various modifications and changes may be madetherein without departing from the broader spirit and scope of theinvention as set forth in the appended claims. For instance, the dataprocessing units 20 may share the connection, e.g. the data connections30,31, to the central control unit 10. Thereby, the central control unitcan send the same synchronisation signal to the data processing units 20simultaneously. In the example of FIG. 1, as mentioned, the dataprocessing units 20 are connected to the central control unit 10 via abus-connection. As shown in the example of FIG. 1, for instance, thedata connections 30,31 may form a bus connection between the centralcontrol unit 10 and the, decentralized, data processing units 20. Thebus connection may for example be a parallel bus or a serial bus.However, other types of connections are also possible, such as forexample a point-to-point connection in which each data processing unit20 is connected by a separate connection to the central control unit 10.

Also, in the example of FIG. 4, the transistors T10,T20 are drawn asfield effect transistors, of which the gate G10,G20 is used as a controlterminal and the sources S10,S20 and drains D10,D20 are connected to thedata connection 30, voltage supply and ground respectively and formrespective signal terminals. However, other types of transistors, suchas bipolar transistors, may be used and be connected in a differentmanner to control the current drawn from the data connection and tocontrol the voltage of the data connection.

Also, the invention is not limited to physical devices or unitsimplemented in non-programmable hardware but can also be applied inprogrammable devices or units able to perform the desired devicefunctions by operating in accordance with suitable program code. Theinvention may also be implemented in a computer program for running on acomputer system, at least including code portions for performing stepsof a method according to the invention when run on a programmableapparatus, such as a computer system or enabling a programmableapparatus to perform functions of a device or system according to theinvention. Such a computer program may be provided on a data carrier,such as a CD-ROM or diskette, stored with data loadable in a memory of acomputer system, the data representing the computer program. The datacarrier may further be a data connection, such as a telephone cable or awireless connection.

The central control unit 10 and/or the data processing unit 20 may beprovided separately. It is also possible to provide a kit of parts, e.g.a central control unit 10 and one or more data processing units 20 whichcan be assembled into a data communication system 1, such as forinstance into the example of a system shown in FIG. 1.

Furthermore, the devices may be physically distributed over a number ofapparatuses, while functionally operating as a single device. Forexample, the central control unit 10 may be implemented as anarrangement of discrete components connected to each other to operate asthe central control unit 10. Also, devices functionally forming separatedevices may be integrated in a single physical device. For example, theelectrical circuit shown in FIG. 3 can be implemented in a singleintegrated circuit.

However, other modifications, variations and alternatives are alsopossible. The specifications and drawings are, accordingly, to beregarded in an illustrative rather than in a restrictive sense.

In the claims, any reference signs placed between parentheses shall notbe construed as limiting the claim. The word ‘comprising’ does notexclude the presence of other elements or steps then those listed in aclaim. Furthermore, the words ‘a’ and ‘an’ shall not be construed aslimited to ‘only one’, but instead are used to mean ‘at least one’, anddo not exclude a plurality. The mere fact that certain measures arerecited in mutually different claims does not indicate that acombination of these measures cannot be used to advantage.

1. A data communication system, including: at least one data processingunit; at least one central control unit; at least one data connectionconnecting said data processing unit to said central control unit; saidcentral control unit including a synchronisation unit for outputting viasaid data connection an electric synchronisation signal to said dataprocessing unit; said data processing unit including a data generatorfor generating data and transmitting, after said electricsynchronisation signal, data to said central control unit; wherein saidcentral control unit further includes a discharge signal generator foroutputting via said data connection to said data processing unit adischarge signal which discharges the data connection chargedelectrically by the electric synchronization signal.
 2. A datacommunication system as claimed in claim 1, wherein said central controlunit further includes: a sensor for sensing a parameter of said dataconnection and/or said data processing unit; and a signal generatorcontrol unit connected to said sensor and said discharge signalgenerator, for controlling outputting said discharge signal based onsaid sensed parameter.
 3. A data communication system as claimed inclaim 2, wherein said sensor includes a voltage sensor for sensing thevoltage of said data connection and said signal generator control unitis connected to controls the discharge signal generator to output thedischarge signal in relationship with the sensed voltage.
 4. A datacommunication system as claimed in claim 2 wherein the signal generatorcontrol unit is connected to control the discharge signal based on adifference between a value of the sensed parameter and a referencevalue.
 5. A data communication system as claimed in claim 2, including acircuit in which at least two of said sensor, said discharge signalgenerator and a synchronisation signal generator are combined.
 6. A datacommunication system as claimed in claim 1, wherein said data processingunit includes at least one sensor.
 7. A data communication system asclaimed in claim 6, wherein said sensor includes an accelerationsensitive sensor and/or a pressure sensor.
 8. A data communicationsystem as claimed in claim 1, wherein said synchronisation signalincludes a voltage signal.
 9. A central control unit for a system asclaimed in claim
 1. 10. A data processing unit for a system as claimedin claim
 1. 11. An occupant protection system, including a sensor systemas claimed in claim 1 and at least one occupant protection deviceconnected to said central control unit, wherein said central controlunit is arranged to control said occupant protection device based ondata received from said data processing unit.
 12. A vehicle including anoccupant protection system as claimed in claim
 11. 13. A method forcommunicating data in a data communication system, said system includingat least one data processing unit, a central control unit, and at leastone data connection connecting said data processing unit to said centralcontrol unit, the method including: said central control unitperiodically outputting an electric synchronization signal over the dataconnection to the data processing unit interface; said data processingunit transmitting, after the electric synchronization signal, data viathe data processing interface to the central control unit; wherein saidcentral control unit outputs a discharge signal via said data connectionto said data processing unit interfaces, for discharging the dataconnection charged electrically by the electric synchronization signal.14. (canceled)
 15. A data communication system as claimed in claim 3,wherein the signal generator control unit is connected to control thedischarge signal based on a difference between a value of the sensedparameter and a reference value.
 16. A data communication system asclaimed in claim 3, including a circuit in which at least two of saidsensor, said discharge signal generator and a synchronisation signalgenerator are combined.
 17. A data communication system as claimed inclaim 4, including a circuit in which at least two of said sensor, saiddischarge signal generator and a synchronisation signal generator arecombined.
 18. A data communication system as claimed in claim 2, whereinsaid data processing unit includes at least one sensor.
 19. A datacommunication system as claimed in claim 3, wherein said data processingunit includes at least one sensor.
 20. A data communication system asclaimed in claim 2, wherein said synchronisation signal includes avoltage signal.
 21. A data communication system as claimed in claim 3,wherein said synchronisation signal includes a voltage signal.